Currently, as is well known, crystals of L-glutamic acid are produced in Japan, United States of America, and other countries, in the form of crystals of the free acid, as they are, or its salts such as the sodium salt and the like, by a so-called fermentation process, for the purpose of using as seasonings, medicaments, foods, drinks, raw materials for synthetic fiber, and the like.
By the way, primary crystals of L-glutamic acid produced by a so-called fermentation process, i.e., crystals of L-glutamic acid obtained by culturing a microorganism having an ability of forming and accumulating L-glutamic acid, followed by separating the accumulated crystals from the fermentation broth, contain, in many cases, various impurities. Therefore, when the monosodium salt (crystal) of L-glutamic acid is to be produced by neutralizing such primary crystals as they are, the primary crystals may exert a large load on filtration, de-coloration, and crystallization of the monosodium salt of L-glutamic acid, in the production process of the monosodium salt of L-glutamic acid.
Because of this, as a method of purifying such crude crystals (primary crystals) of L-glutamic acid, there has been hitherto proposed a method of heating crude crystals of L-glutamic acid in an aqueous solvent to transform the α crystals (crystals having short rod shape or granular shape) into the β crystals (crystals having needle shape or scale-like shape), during which transformation course the impurities in the crude crystals of L-glutamic acid are released, and isolating the resulting purified crystals of L-glutamic acid from the mother liquor (Japanese Patent Publication Nos. 4730/1970 and 13806/1970, and so forth).
However, the following two problems arise in the transformation or transition recrystallization method. That is, (1) the transition may sometimes take a long period of time owing to the effects of the impurities. Additionally, (2) a long time heating may, in turn, sometimes induces the loss of L-glutamic acid owing to deterioration of L-glutamic acid (the formation of pyrrolidonecarboxylic acid (PCA) through dehydration reaction of L-glutamic acid).